1. Field of the Invention
The present invention relates to polymeric polyamines and a method for stabilizing Ag nanoparticles by employing the same. The produced Ag nanoparticles are in the form of silver slurry, silver gel or solid, and suitable for composite material or antimicrobial material. Fields of the present invention include electric industries, for example, conductive silver nanowires, parts and sensors, and biomedicine or medicinal industries. In addition, the Ag nanoparticles have both hydrophilic and hydrophobic properties and therefore can be dissolved in water and organic solvents, and are compatible with many kinds of polymers. Therefore, the product of the present invention is a good polymeric surfactant or dispersant suitable for dispersing nanoscale particles, for example, pigments and silver particles.
2. Related Prior Arts
The application of Ag nanoparticles is one of the most important technologies in this century. The traditional methods for producing water solutions of Ag nanoparticles are primarily to reduce silver nitrate or other silver salts with organic surfactants, dispersants or stabilizers for stabilizing the Ag nanoparticles. To exhibit good effects in antimicrobial, pharmaceutical, biomedicine and electrical applications, the Ag particles have to keep in the nanoscale and large surface areas without aggregation. Therefore, it's very important to control size of the Ag particles in the nanoscale and maintain thermal stability thereof.
In processes for producing Ag nanoparticles, organic surfactants or stabilizers are an important operation factor. In addition, most silver slats, for example, silver nitrate, is more easily dissolved in water than organic solutions, and therefore the product is usually prepared in water solution. That is, the existing conditions will restrict applications of the Ag nanoparticles.
The above problems have been discussed in some reports. In J. Phys. Chem. B 1998, 102, 10663-10666, the Ag particles are prepared in water solution and stabilized with molecular chains of sodium polyacrylate or polyacrylamide. In Chem. Mater. 2005, 17, 4630-4635, thioalkylated poly(ethylene glycol) is used as a stabilizer for stabilizing Ag particles in water. In Langmuir 1999, 15, 948-951, 3-aminopropyltrimethoxysilane (APS) is used as a stabilizer and N,N-dimethylformamide is used to reduce silver ions in water. In J. Phys. Chem. B 1999, 103, 9533-9539, sodium citrate is used to prevent the Ag particles from aggregation or agglomeration which results in larger particle size, wider size distribution or multiple-peak distribution. In Langmuir 1996, 12, 3585-3589, some nonionic surfactants (polyethylene oxide or ethoxylated block) are used to stabilize Ag nanoparticles which are in the form of gel-type particles covered with molecular chains of the surfactant, the examples include poly-(10)-oxyethylene oleyl ether and Tween 80 (polyoxyethylene-(20)-sorbitan monooleate) (available from Sigma). In Langmuir 1997, 13, 1481-1485, NaBH4 is used as a reducing agent, and the reaction equation is:2AgNO3+2NaBH4+6H2O→2Ag+2NaNO3+2H3BO3+7H2 In this reaction, the stabilizers are cetyltrimethylammonium bromide (CTAB) as a cationic surfactant, sodium dodecyl sulfate (SDS) as an anionic surfactant and poly(oxyethylene) isooctylphenyl ether-TX-100 as a nonionic surfactant.
As described in the above, the traditional method for stabilizing Ag particles is to add surfactants or stabilizers. However, the solutions of such Ag particles have solid contents less than 10% and can not be in the form of silver slurry, or have a higher solid content with aggregation.